Kaolin is a fine, usually white clay formed by the weathering of aluminous minerals (as feldspar) and mainly consists of kaolinite. Kaolinite is commonly represented by one or more of the chemical formulae Al4Si4O10(OH)8; Al2O3.2SiO2.2H2O; and/or Al2Si2O5(OH)4. Kaolin is one of the many industrial minerals mined today. Reserves are found in Georgia (USA), Egypt, Brazil, United Kingdom, Queensland (Australia), Korea, China, and Ukraine.
Generally speaking, kaolin from different countries, and even different deposits within the same country, differs in many respects due to variations in a number of kaolinite properties. Examples of such properties include degree of crystallinity, coarseness, brightness, levels of other compounds such as titania and iron oxide, particle size, particle shape, size and/or shape distribution. Variations in properties leads to differences in performance of the resultant kaolin products. For example, crystallinity impacts resultant brightness, whiteness, opacity, gloss, and viscosity of the resultant products. It is noted that opacity and gloss are application performance parameters while the other listed parameters are pigment attribute parameters. Particle size, shape, and distribution impacts the smoothness, optical properties, and flow properties of the resultant products. Smoothness and optical properties are application performance parameters while flow properties are pigment attribute parameters.
The greatest demand for kaolin based products comes from the paper industry, which uses them to coat and fill papers and boards. However, kaolin based products include paints, agricultural compositions, fiberglass products, polymer and rubber compositions, ceramic applications, catalyst supports, pharmaceuticals, cosmetics, electrical components, adhesives, filter aids, and many more. Certain grades of kaolin having discrete properties are ideally suited for select applications. Accordingly, to maximize the quality of a resultant kaolin grade, kaolin crude is subjected to processing that yields a specifically desired grade of kaolin. Moreover, a specifically identified kaolin crude is often selected when a certain desired grade of kaolin is made, again to maximize the quality of that grade of kaolin.